Conventional light transmission systems used for vehicle head lights or tail lights typically use a bulb and reflector system. In a bulb and reflector system the filament of the bulb is placed at or near a focal point of a parabolic reflector. The light emitted by the bulb filament is collected by the reflector and reflected outward to form a light beam. A lens is used to shape the light beam into a specified pattern to satisfy vehicle lighting specifications. Typically, in an automotive application, a conventional bulb and reflector system collects and reflects only thirty percent of the light emitted from the bulb filament into the useful lighting area.
Bulb and reflector systems have several disadvantages, including aerodynamics and aesthetic styling; e.g., the depth of the reflector along its focal axis and the height of the reflector in directions perpendicular to the focal axis greatly limited attempts at streamlining vehicle contours. Additionally, thermal energy given off by the bulb during operation must be considered and the size of the reflector as well as the material used in its construction vary depending upon the amount of thermal energy generated by the bulb filament. Decreasing the size of the reflector requires use of materials with high thermal resistivity for the reflector.
One approach to develop an automotive lighting system for use with the newer streamlined body designs is proposed in U.S. Pat. No. 5,434,754, assigned to the assignee of the present invention, which discloses the combination of a fiber optic light guide which transmits light from a remote light source, through a light manifold, and to a reflector. There are a number of problems associated with such an approach. First, remote lighting to date is typically a high intensity discharge source coupled with a reflector. The light is focused into a large diameter light guide which transmits the light to the desired location. The high intensity discharge source produces a substantial amount of heat which tends to degrade the light guide. Environmental factors have a further degrading effect on conventionally used light guides. The light guide typically must be 8-12 mm thick in order to capture the requisite amount of light from the source. These guides are very expensive and difficult to work with. Further, this structure requires assembly of a lens, a multifaceted reflector, and a manifold portion to form the vehicle tail light. Also, the manifold portion must be indexed relative to the reflector portion. The manifold is required to expand the incoming light for distribution across the lamp surface. This results in a substantial portion of unlit area required for the manifold and hence a larger foot print of the overall lamp, which results in lighting design inflexibility.
A laser illuminated thin sheet optical element lighting device as disclosed in attorney docket no. 196-0014 entitled Laser Illuminated Lighting System, assigned to the assignee of the present invention, addressed a number of deficiencies in the vehicle lighting arts. However, problems still remain, one of these problems being the large amount of unlit area required for the manifold portion. Also, when using laser light, the light transmitted will vary in intensity from the cross sectional center to the perimeter of the light beam. The intensity variation must be accounted for when designing the manifold section to avoid hot spots of illumination across the lamp surface, adding design cost to the lighting assembly.
Therefore, it would be desirable to provide a laser illuminated, unitary thin sheet optic tail lamp assembly for a vehicle which accommodates manufacturing and thermal considerations as well as the space limitations dictated by vehicular aerodynamic and styling requirements.